Field of the Invention
The present invention relates to an exposure method in an electronic copying machine or the like where a discharge lamp energized by an alternating electric current is used as a light source, and more particularly to an improved method for compensating for periodic variations, which occur in the exposure amount of a sensitive material or sensitive paper (hereinafter referred to as sensitive member) due to periodic output variations of the discharge lamp.
In an electronic copying machine or the like using an a-c discharge lamp as a light source, an a-c stabilizer for the discharge lamp is employed. Since the output of an a-c stabilizer for the discharge lamp is a periodic function, the output light intensity of the discharge lamp also varies in accordance with the periodic output variations of the stabilizer where FIG. 1 illustrates the periodic output variations of the discharge lamp, the frequency of the FIG. 1 signal being the same as the energizing alternating current for the distance lamp. Consequently, when exposing a sensitive member for copying purposes, the amount of exposure periodically varies in accordance with the periodic variations occurring in the output intensity of the discharge lamp. Thus, certain shortcomings tend to arise such as periodic fogging of the background of the copied image and periodic changes in the optical density of the image itself. Such phenomena tend to appear more conspicuous as the sensitive member scanning speed increases.
Although the above disadvantages are removable by means of high-frequency lighting or direct-current lighting, the former is not economically desirable as it requires a special power source or a high-frequency converter, while the latter is inferior in overall efficiency and tends to introduce a problem of darkening.